Arabic Abstract

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English Abstract

Current-Voltage measurements in the presence of a small magnetic field have been preformed on high quality samples of Y₁₂₃ and Y₁₂₃(Ag₂O)[x] Hi-T[c] superconductors, to study the behaviour of the critical currents, pinning forces and flux flow resistance (FFR) near T[c]. The addition of Ag₂O enhances the critical currents and reduces the flux flow resistance in all flux flow regions. Moreover FFR exhibits a broad minimum at low temperatures, then diverges near T[c]. This minimum becomes sharper in the field cooled states of Y₁₂₃, and occurs at fields near B[c]. The field cooled pinning forces follow a scaling behaviour (near T[c]) as a function of the reduced field B/B[c₂]. Furthermore, Viscosity coefficient n, deduced from the FFR and Kim's model, displays sharp peaks for different Ag₂O concentrations x, with sharper peaks for higher x. Viscosity coefficient n versus temperature exhibits broad maximum at low temperatures and decreases rapidly close to T[c].